2001 - S500

I know the instrument cluster lighting is dimmed or brightened automatically to suit daylight conditions. I'm a little confused about the Instrument Cluster Illumination at night. The instrument cluster as well as the COMAND seems to get dimmer at night, but if I happened to turn on the interior lights the instrument cluster seems to get brighter. I always thought that the illumination should be the brightness when the interior is at its darkest. I only had the car a few weeks so I'm not sure what’s normal.